Backport additional kwargs tweaks from 10

Author: headius

core/src/main/java/org/jruby/ir/runtime/IRRuntimeHelpers.java

@@ -739,12 +739,12 @@ private static IRubyObject receiverSpecificArityKwargsCommon(ThreadContext conte
             // This complicates check_arity but empty ** is special case.
             RubyHash hash = (RubyHash) last;
             return hash;
-        } else if (!isKwarg) {
-            // This is just an ordinary hash as last argument
-            return last;
-        } else {
+        } else if (isKwarg || ((RubyHash) last).isRuby2KeywordHash()) {
             RubyHash hash = (RubyHash) last;
             return hash.dupFast(context);
+        } else {
+            // This is just an ordinary hash as last argument
+            return last;
         }
     }
 

core/src/main/java/org/jruby/ir/targets/indy/InvokeSite.java

@@ -709,7 +709,7 @@ private void finishBinding(CacheEntry entry, MethodHandle mh, IRubyObject self,
 
         NativeCallMethod nativeMethod;
         if (method instanceof AbstractIRMethod) {
-            // Ruby methods with ruby2_keywords don't use formal keywords
+            // Ruby methods handle clearing kwargs flags on their own
             acceptsKeywords = true;
         } else if (method instanceof NativeCallMethod && (nativeMethod = (NativeCallMethod) method).getNativeCall() != null) {
             // native methods accept keywords only if specified